1. Field of the Invention
This invention relates to the measurement of gases dissolved in molten metals. In particular, the instant invention relates to the measurement of hydrogen dissolved in the molten tin bath of a forming chamber used in float glass formation.
2. Prior Art
The formation of glass via the process wherein molten glass is cooled and formed into sheets while on the surface of a molten metal in a forming chamber is well known. It has been perceived that the composition of the molten metal on which the glass is formed may change as gases from the atmosphere and from the glass are dissolved into the molten metal. However, there has been no satisfactory way of measuring the amount of dissolved gas in the molten metal. Without knowledge of dissolved gas in the molten metal, it has not been possible to determine the effects of the changes in the gaseous atmosphere of the forming chamber on the molten metal. The forming chamber generally is maintained with an atmosphere of predominantly nitrogen with some hydrogen. This atmosphere is to prevent oxidation of the tin which is the conventional metal utilized in the forming chamber. The following references are considered pertinent to the apparatus and method of the instant invention.
U.S. Pat. No. 3,855,098 to Fletcher discloses an ionic sensitive electrode comprising a porous inert material of ceramic which carries on its surface a thin ion sensitive membrane to be exposed to a test liquid to develop an electrical potential as the function of the ionic activity or concentration of the test liquid. The porous material provides a mechanical support for the membrane and the porosity of the material serves to define continuous channels to carry electrolyte liquid to the interior surface of the membrane.
In U.S. Pat. No. 2,106,744 to Hood et al and U.S. Pat. No. 3,923,688 to Hammel et al disclose leaching to form porous glasses. However, selectively porous glasses do not have good thermal shock resistance as the porous portions have different thermal expansion characteristics.
U.S. Pat. No. 4,003,818 to Juillard et al discloses a method of obtaining a microporous membrane. The membrane is formed by formation of a paste which has a filler substance which may be removed after the article is formed from the paste. The pore-forming material is removed by solvent or chemical decomposition and may be calcium carbonate, colloidal alumina, metallic oxide or other products capable of solvent or chemical removal.
U.S. Pat. No. 3,896,020 to Le Blanc, Jr. discloses a sensor for measurement of carbon dioxide partial pressure in an aqueous electrolyte solution. The system of Le Blanc, Jr. is limited in that the system is specific to carbon dioxide. Further, the system in using organic materials in several layers is not suitable for high temperature use because of both thermal shock problems and difficulties with decomposition of the organic materials.
Porous sintered ceramic bodies are known, but these can not be formed to be selectively porous such that one portion of a unitary body is gas pervious while another portion is gas impervious.
There is a need for a device for measuring the partial pressure of gas in molten metals that is resistant to thermal shock, easily inserted in the metal, capable of withstanding high temperatures and inexpensive. Presently, there are no systems known to the applicant for accurately measuring partial pressure of gas in a molten metal while the metal remains molten. Further, there is a need for a device to measure partial pressure of gases in the bath of a glass-forming chamber in order to aid in a determination of bath chemistry as it relates to the balancing of bath atmosphere and gaseous additions to the bath. Further, there is a need for a device that permits dissolving gases in a bath by means other than providing an atmosphere above the bath. Further, there is a need for formation of a permeable ceramic body that will allow gases to permeate the body but not allow metals to penetrate.